Methods and apparatus for selective, oxidative patterning of a surface

ABSTRACT

The present invention provides methods and apparatus for selectively patterning surfaces using radical species generated with a photocatalyst. The photocatalyst may comprise a photocatalytic semiconductor or a photosensitizer. The radical species are brought into contact with an oxidizable coating disposed on the surface, thereby locally oxidizing and selectively patterning the surface. The photocatalyst is preferably disposed on a delivery device, such as a stamp, mask, or scanning probe, that is brought into close proximity or contact with the coated surface. The photocatalyst is then excited in a manner capable of generating radical species, for example, oxygen-containing radical species, in appropriate media. It is expected that these radical species will be transferred to the coated surface along a substantially shortest distance path, thereby locally oxidizing and patterning the surface.

REFERENCE TO RELATED APPLICATION

[0001] The present application claims priority and the benefit of thefiling date of provisional U.S. patent application Ser. No. 60/373,879filed Apr. 19, 2002, and takes advantage of that filing date.

FIELD OF THE INVENTION

[0002] The present invention is related to surface patterning. Moreparticularly, this invention is related to methods and apparatus forselectively patterning a surface using radical species, therebyproviding a surface with a specified and controllable gradient ofelectrical, chemical, and/or physical properties.

BACKGROUND OF THE INVENTION

[0003] Electron beam (“e-beam”) lithography has successfully beenemployed in a variety of industrial applications to fabricate very smallstructures. An e-beam is focused on a target substrate to slowly andpainstakingly ‘draw’, ‘carve’, or ablate a very fine pattern into thesubstrate. This procedure is repeated for each substrate required.E-beam lithography typically is capable of producing features having adimension or resolution on the order of nanometers.

[0004] Though often effective, e-beam lithography is prohibitively slowand expensive for many applications, and is not readily applicable tomass-production. Techniques therefore have been developed to lowercosts, decrease production times, and increase reproducibility. One suchtechnique comprises using e-beam lithography to create a master, fromwhich a stamp may be secondarily created. A stamping material (ink) isapplied to the stamp, which is subsequently brought into contact with asurface. The stamping material is transferred to the surface atlocations where the stamp contacts the surface. The surface may then beetched to remove surface material at all points that do not havestamping material, thereby replicating the stamp and selectivelypatterning the surface. Stamping of alkane thiols typically is capableof producing features having a dimension or resolution on the order ofmicrons, though smaller structures are theoretically attainable.

[0005] Stamping of alkane thiols from a stamp onto a gold surface hasbeen extensively investigated. The alkane thiol is absorbed either intoor onto the stamp, and is then brought into contact with the goldsubstrate surface. Alkane thiols commonly consist of close-packed,independent chains that may be chemisorbed to a surface, and which oftenare used to modify surfaces, for example, to alter corrosion resistanceand/or electrical properties, or to pattern the surfaces. Common alkanethiols include octadecanethiol and hexadecanethiol. These materials aretypically applied from solution, e.g. ethanol or hexane, to surfacessuch as gold, silver, or copper.

[0006] Although stamping of alkane thiols on gold surfaces has beenextensively investigated, to date the method is still primarily alaboratory technique that has not been effectively transferred toindustrial settings, due to the complexities of the stamping process.The simultaneous and often contradictory requirements of rapid diffusionand high solubility of the alkane thiol onto the stamp, appropriatemechanical characteristics of the stamp, fast reaction rates relative tosurface diffusion rates of the alkane thiol onto the gold substrate,high irreversibility on the gold surface, and resistance of the stampingmaterial to subsequent processing steps have been difficult to achieve.Thus, a central factor limiting adaptation of the laboratory techniqueto industrial applications has been the difficulties encountered whiletrying to achieve simultaneous control of multiple time-dependent, orrate, processes.

[0007] A newer surface patterning technique that has been developed tolower costs and decrease production times associated with e-beamlithography employs e-beam, V, or x-ray resists. Such resists, andtechniques for manufacturing them, are found, for example, in U.S. Pat.Nos. 4,717,645 to Kato et al.; 4,795,692 to Anderson et al.; and4,868,241 to Hiscock et al.; all of which are incorporated herein byreference. A common resist technique comprises coating a substrate witha material that is sensitive to e-beam, UV, or x-ray radiation. Thecoating is selectively exposed to radiation, for example, with a focusedelectron beam that ‘traces’ the required pattern on the coating.Irradiation removes the coating at the point of exposure and provides aselectively patterned surface. This technique is similar to traditionale-beam lithography, except that the affected material comprises only avery thin, typically organic coating, thereby reducing the amount ofmaterial that is removed and the amount of time required to achievepatterning. The size of features attainable using resists depends on theenergy source used for irradiation.

[0008] A significant drawback of resist techniques is that, althoughmore rapid than traditional e-beam lithography techniques, time- andcost-intensive patterned irradiation of resists must still be conductedindividually for each patterned surface. This drawback significantlylimits the industrial viability of e-beam and x-ray resists.

[0009] Yet another technique that reduces the costs and production timesassociated with e-beam lithography is photolithography. Photolithographywas developed prior to e-beam techniques, but provides many of thebenefits of stamping and resist techniques. Photolithography typicallyrequires production of a Master mask. The mask is placed over asubstrate that has been coated with a photosensitive resist. A lightsource is shone through the patterned mask onto the resist, therebypatterning the surface. With a positive resist, material may be easilyremoved at all points on the surface that are exposed to irradiation.With a negative resist, material may be removed at all points notirradiated.

[0010] Although photolithography provides many of the benefits of e-beamlithography in a rapid and low cost procedure, the technique hasfundamental limits. Specifically, photolithography typically cannotpattern surface structures having a size much smaller than thewavelength of the incident light. When using an i-line standard (365 nmUV light generated with mercury lamps) energy source, features on theorder of about 500 nm are possible. Advanced focusing techniques mayallow features slightly smaller than the wavelength of the incidentlight, for example, features as small as 300 nm with the i-linestandard, but significantly smaller features are not possible.

[0011] Researchers have also examined the possibility of patterning withdeep UV (“DUV”) light having a wavelength of 248 nm, generated with akrypton fluoride (“KrF”) excimer laser energy source 18. Furthermore,researchers have explored 193 nm laser sources 18, such as argonfluoride (“ArF”) excimer lasers. Researchers are still further exploring157 nm laser sources 18, in the hopes of patterning surface features onthe order of about 100 nm, when using advanced focusing techniques.However, systems using focusing techniques and operating at or belowabout 193 nm may suffer from degraded optics, since most lens materials,including fused silica or quartz, are absorptive at these wavelengths.Density variations in materials are also a problem at or below about 193nm. Exotic alternative lens materials therefore are being examined,including, for example, calcium fluoride. Although calcium fluoride ishighly transmissive, a significant drawback is that it is very difficultto fabricate. Additionally, if extreme UV (13 nm) or X-ray (<3 nm) arelight sources ever considered for mass-production purposes, such as inthe production of microelectronics, it is expected that complex andcost-intensive new lasers or synchrotron systems will be required togenerate adequate extreme UV or X-ray photons to meet productionrequirements.

[0012] Especially in the field of microelectronics, the drive forsmaller and smaller structures is rapidly creating a need to patternsurface structures smaller than those possible today with standardphotolithography employing i-line standard UV light. In many cases,traditional e-beam techniques are the only practical recourse forproviding such fine structures.

[0013] In view of the drawbacks associated with prior art patterningtechniques, it would be desirable to provide methods and apparatus forpatterning surfaces that overcome these drawbacks.

[0014] It would be desirable to provide methods and apparatus thatreduce costs and production times, as compared to e-beam techniques.

[0015] It also would be desirable to provide methods and apparatus forpatterning surfaces that require control of fewer rate processes.

[0016] It would be desirable to provide methods and apparatus forpatterning surfaces that may be replicated using a stamping or maskingtechnique.

[0017] It would be desirable to provide methods and apparatus thattheoretically enable patterning of surface structures having a sizesmaller than achievable with standard photolithography techniques.

[0018] It would be desirable to provide methods and apparatus that areapplicable to industrial applications.

SUMMARY OF THE INVENTION

[0019] In view of the foregoing, it is an object of the presentinvention to provide methods and apparatus for patterning surfaces thatovercome drawbacks associated with prior art techniques.

[0020] It is an object to provide methods and apparatus that reducecosts and production times, as compared to e-beam techniques.

[0021] It is another object of the present invention to provide methodsand apparatus that require control of fewer rate processes.

[0022] It is yet another object to provide methods and apparatus forpatterning surfaces that may be replicated using a stamping or maskingtechnique.

[0023] It is still another object to provide methods and apparatus thattheoretically enable patterning of surface structures having a sizesmaller than achievable with standard photolithography techniques.

[0024] It is an object to provide methods and apparatus that areapplicable to industrial applications.

[0025] These and other objects of the present invention are accomplishedby patterning a surface using radical species generated with aphotocatalyst, for example, a photocatalytic semiconductor, aphotosensitizer, or a combination thereof. The radical species areselectively brought into contact with an oxidizable coating disposed onthe surface.

[0026] In a preferred embodiment, the oxidizable surface coating isadsorbed onto the surface. The coated surface is preferably immersed ina medium capable of generating radical species in the presence ofelectron hole pairs or excited molecules, for example, an oxygen- ornitrogen-containing medium. The medium may be either organic orinorganic and is preferably fluidic, for example, a gaseous medium, aliquid medium, an aqueous medium, a gel, water, or air. Furthermore, themedium preferably comprises an oxidant, such as oxygen, nitrogen,oxidizing ions, Redox species, Redox mediators, or electron transferagents. The medium may also or alternatively contain stabilizing agents,such as selenium, zinc, lipoic acid, methionine, cysteine, or N,NDimethyl glycine. As yet another alternative, the medium may comprisemore inert conditions, such as vacuum or Argon gas. Other mediums willbe apparent to those of skill in the art.

[0027] A stamp or mask, formed, for example, using traditional e-beamlithography techniques, per se known, is brought into close proximity orcontact with the coated surface. The mask comprises a patterned layer ofmaterial that is capable of generating radical species, for example, apatterned photocatalyst layer. When the photocatalyst comprises aphotocatalytic semiconductor, TiO₂ is a preferred photocatalyticsemiconductor, but others, such as SnO₂, or an InTaO₄ compound dopedwith Ni, will be apparent to those of skill in the art and are includedin the scope of the present invention. When the photocatalyst comprisesa photosensitizer or photosensitizing agent, preferred photosensitizersinclude photofrins, texaphyrins, metallotexaphyrins, porphyrins,hematoporphyrins, chlorins, bacteriochlorins, phthalocyanines andpurpurins. Additional photosensitizers will be apparent to those skilledin the art and are included in the present invention.

[0028] Next, an energy source is exposed through the mask/stamp to thepatterned photocatalyst layer. It is expected that the photocatalystwill generate radical species in appropriate environments upon exposureto the energy source. When the photocatalyst comprises a photocatalyticsemiconductor, preferred light sources include UV or x-ray lamps orlasers. Other light sources will be apparent to those skilled in theart. Energy from the light source generates electron hole pairs in/onthe patterned photocatalytic semiconductor layer, for example, in apatterned layer of TiO₂. The electron hole pairs generate radicalspecies, such as oxygen-containing radical species, in appropriateenvironments.

[0029] When the photocatalyst comprises a photosensitizer, preferredlight sources include visible light sources, such as lights sources withwavelengths between about 550-850 nm, for example, a visible laser lightsource, such as a Helium Neon (“HeNe”) laser. Other light sources, suchas UV light sources, will be apparent. Energy from the light sourceexcites the photosensitizer from a ground state to a singlet excitedstate. The singlet may decay to an intermediate triplet excited state,which is able to transfer energy to another triplet. Some molecules havea triplet ground state, for example, oxygen or O₂. Thus, energy may betransferred from the photosensitizer in the excited triplet state to thetriplet ground state molecule, thereby exciting the molecule to asinglet state. A radical-generating reaction may then be achieved withthe excited singlet state molecule, for example, a reaction generatingoxygen-containing radical species. Other molecules capable of formingradical species upon exposure to an excited photosensitizer will beapparent to those of skill in the art, for example, thiohydroxamicesters.

[0030] Regardless of whether the patterned photocatalyst layer comprisesa patterned photocatalytic semiconductor layer or a patternedphotosensitizer layer, it is expected that radical species generated atthe patterned photocatalyst layer will be transferred to the coatedsurface along a substantially shortest distance path. Thus, only areason the coated surface that are in close proximity to the patterned layerof the mask/stamp will come into contact with the radical species. Sincethe surface coating is oxidizable, it is expected that these areas willoxidize locally, thereby patterning the surface. Portions that are notcontacted by the radical species are not expected to oxidize. It shouldalso be noted that oxidation may be possible with excited singlet ortriplet state molecules, in addition to radical species.

[0031] Techniques of the present invention potentially may be used incombination with prior art photosensitive resists. Such local patterningthrough chemical modification of the coating is expected to alter thereactivity of the coating, and may either stabilize or destabilize theaffected portion of the coated surface. Unaffected adsorbed materialoptionally may be used for a second chemical step, for example, a secondmasking step.

[0032] An expected advantage of the present invention, as compared toprior art photolithography techniques, is that the patternedmask/stamp's photocatalyst layer will enable patterning of features onthe coated surface that are significantly smaller than the wavelength oflight generated by the energy source. When using a photocatalyticsemiconductor, this is possible because electron hole pairs generated inthe photocatalytic semiconductor layer have a dimension on the order ofsub-Angstroms, as compared to the incident light that generates theelectron hole pairs, which has a dimension on the order of nanometers.Likewise, when using photosensitizers, the radical species generatedwith the photosensitizers by quanta of energy transmitted to molecules,are expected to be significantly smaller than the wavelength of incidentlight.

[0033] An alternative embodiment of apparatus in accordance with thepresent invention comprises a scanning probe having a photocatalyst tip.An energy source is coupled to the tip, for example, via fiber optics ornear-field optical microscopy, such that radical species may begenerated locally at the tip. By scanning the probe over an oxidizablesurface coating while creating radical species, a selectively patternedsurface may be formed.

[0034] It is expected that the present invention may be used inconjunction with a variety of oxidizable surface coatings. In a firstembodiment, the surface coatings comprise alkane thiols. In a secondembodiment, the coatings comprise thioethers. In a third embodiment, thecoatings comprise unsaturated materials. Saturated materials are alsocontemplated. In a fourth embodiment, the coatings comprise metaloxides. Bare metal substrates may also be used. Other coatings will beapparent to those skilled in the art.

[0035] The present invention may be applicable to a variety of fieldsranging from fabrication of microelectronics, computer chips, biomedicalassays, physical research (e.g. top gates and quantum dots or wells),and combinatorial chemistry. Additional applications will be apparent tothose of skill in the art, and are included in the present invention.

[0036] Methods and apparatus for accomplishing the present invention areprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Further features of the invention, its nature and variousadvantages will be more apparent from the accompanying drawings and thefollowing detailed description of the preferred embodiments, in whichlike reference numerals refer to like parts throughout, and in which:

[0038]FIG. 1 is a schematic representation of a prior art technique forperforming photolithography;

[0039] FIGS. 2A-2C are schematic representations of photocatalystreactions leading to generation of radical species; FIGS. 2A and 2Bdepict the formation of electron hole pairs in a photocatalyticsemiconductor, while FIG. 2C depicts excitation of a photosensitizer;

[0040] FIGS. 3A-3D are schematic representations of chemical reactionsdemonstrating oxidation of a surface coating in the presence of radicalspecies;

[0041] FIGS. 4A-4C are schematic representations of a first embodimentof apparatus constructed in accordance with the present invention;

[0042]FIGS. 5A and 5B are schematic representations of a method ofpatterning a surface in accordance with the present invention, utilizingthe apparatus of FIG. 4;

[0043]FIGS. 6A and 6B are a schematic representation of an alternativeembodiment of apparatus constructed in accordance with the presentinvention;

[0044]FIGS. 7A and 7B are schematic representations of a method ofpatterning a surface in accordance with the present invention, utilizingthe apparatus of FIG. 6A;

[0045]FIG. 8 is a schematic representation of yet another alternativeembodiment of apparatus constructed in accordance with the presentinvention;

[0046] FIGS. 9A-9C are schematic representations of a method ofpatterning a surface in accordance with the present invention, utilizingthe apparatus of FIG. 8; and

[0047] FIGS. 10A-10E are schematic representations of exemplary surfacepatterns that it is expected may be formed utilizing the methods andapparatus of the present invention; FIG. 10 are overhead views, exceptfor FIG. 10C, which is a side view.

DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention is related to surface patterning. Moreparticularly, this invention is related to methods and apparatus forselectively patterning a surface using radical species, therebyproviding a surface with a specified and controllable gradient ofelectrical, chemical, and/or physical properties.

[0049] With reference to FIG. 1, a prior art technique for performingphotolithography is described. Substrate 10 comprises surface 12 havingoxide 14 and photosensitive resist coating 15. Mask 16, havingtransparent pattern section 17 and opaque masking section 18, isdisposed above oxide 14 and coating 15, while energy source 19 isdisposed above mask 16. Energy source 19 typically comprises a UV orx-ray energy source.

[0050] A common technique for forming substrate 10 with surface 12,oxide 14, and photosensitive resist coating 15 comprises providing adoped silicon substrate 10. Oxide 14 is then grown on substrate 10. Nextphotoresist 15 is spun-coated onto the oxide.

[0051] With mask 16 disposed between surface 12 and energy source 18,the energy source is activated and irradiates mask 16 with incidentlight 20. Incident light 20 passes through mask 16 along pattern section17, and contacts photosensitive resist coating 15 in a pattern 17′.Pattern 17′ replicates pattern section 17 of mask 16 on surface 12.Masking section 18 inhibits transmission of light 20 to surface 12.

[0052] Resist coating 15 may be either a positive or a negative resistcoating. With positive resist coating PR, coating 15 may be easilyremoved at all points on surface 12 disposed within pattern 17′ that areexposed to irradiation, for example, via a developing procedure. Withnegative resist NR, material may be removed at all points on surface 12that are not disposed within pattern 17′, again via a developingprocedure. Oxide 14 may then be removed at all points wherephotosensitive resist coating 15 has been removed, for example, via asecondary etching procedure. Selective removal of oxide 14 providesselectively patterned surfaces 12′ and 12″, respectively.

[0053] Although photolithography provides many of the benefits of e-beamlithography in a rapid and low cost procedure, the technique hasfundamental limits. Specifically, photolithography typically cannotpattern surface structures having a size much smaller than thewavelength of the incident light from energy source 18. This means thatthe minimum size of structures contained within pattern 17 of mask 16must be close to the dimensions of the wavelength of the incident light,and the resultant selective pattern 17′ formed on surface 12 will nothave any structures significantly smaller or finer than the structureswithin mask pattern 17.

[0054] When using an i-line standard (365 nm UV light generated withmercury lamps) energy source 18, features on the order of about 500 nmare possible. Advanced focusing techniques may allow features orstructures slightly smaller than the wavelength of the incident light,for example, features as small as 300 nm, but features significantlysmaller than the wavelength of the incident light have not beenachieved. Structures on the order of 300-500 nm may not be sufficient ina variety of applications, including microelectronics. Thus, expensiveand time-consuming e-beam techniques may be required.

[0055] Researchers have also examined- the possibility of patterningwith deep UV (“DUV”) light having a wavelength of 248 nm, generated witha krypton fluoride (“KrF”) excimer laser energy source 18. Furthermore,researchers have explored 193 nm laser sources 18, such as argonfluoride (“ArF”) excimer lasers. Researchers are still further exploring157 nm laser sources 18, in the hopes of patterning surface features onthe order of about 100 nm, when using advanced focusing techniques.However, systems using focusing techniques and operating at or belowabout 193 nm may suffer from degraded optics, since most lens materials,including fused silica or quartz, are absorptive at these wavelengths.Density variations in materials are also a problem at or below about 193nm. Exotic alternative lens materials therefore are being examined,including, for example, calcium fluoride. Although calcium fluoride ishighly transmissive, a significant drawback is that it is very difficultto fabricate. Additionally, if extreme UV (13 nm) or X-ray (<3 nm) arelight sources ever considered for mass-production purposes, such as inthe production of microelectronics, it is expected that complex andcost-intensive new lasers or synchrotron systems will be required togenerate adequate extreme UV or X-ray photons to meet productionrequirements.

[0056] Referring now to FIGS. 2 and 3, prior to discussion of apparatusand methods in accordance with the present invention, reactionsencountered while practicing the present invention are described.Although these reactions are believed to be the mechanism by which thepresent invention may be practiced, the present invention is primarilyconcerned with the end result, i.e. patterning. Thus, the reactions andpurported mechanism are provided only for the benefit of the reader andshould in no way be construed as limiting.

[0057] With reference to FIG. 2, photocatalyst reactions leading togeneration of radical species are described. FIGS. 2A and 2B depict theformation of an electron hole pair in a photocatalytic semiconductoratom, with subsequent generation of radical species. FIG. 2C depictsexcitation of a photosensitizer.

[0058] In FIG. 2A, photocatalytic semiconductor atom S is disposed in anoxygen-containing medium M, for example, H₂O ). Semiconductor atom S iscontacted by energy quanta E₁ having an excitation energy below the bandgap energy of semiconductor atom S. As an illustrative example, the bandgap energy for photocatalytic semiconductor TiO₂ is about 3.2 eV. Sinceenergy quanta E₁ has an excitation energy below the band gap ofsemiconductor atom S, the quanta does not generate an electron hole pairin semiconductor atom S.

[0059] In FIG. 2B, semiconductor atom S is contacted by energy quanta E₂having an excitation energy above the band gap of semiconductor atom S.Energy quanta E₂ releases electron e and hole h within semiconductor S,which are collectively referred to as electron hole pair H. Electronhole pair H migrates to atom/medium interface I. Electron e and hole hinteract with oxygen contained within medium M, thereby formingoxygen-containing radical species R₁ and R₂. R₁ is a hydroxyl radical,while R₂ is a super-anion oxide radical. Radical species R₁ and R₂ havecross-sections on the order of Angstroms or smaller. After a briefperiod, electron hole pairs that don't form radical species recombine.

[0060] For the exemplary embodiment of a TiO₂ photocatalyticsemiconductor atom S exposed to energy quanta E₂ from a UV energysource, while immersed in fluid medium M comprising H₂O, the equationsgoverning generation of radical species are as follows:

TiO₂+UV→e+h   (1)

h+OH—→*OH   (2)

e+O₂→O₂*—  (3)

O₂*—+H₂O →HO₂*+OH—  (4)

[0061] where ‘*’ denotes a radical species. This provides an overallreaction via TiO₂ catalysis of:

UV+O₂+H₂O→HO₂*+*OH   (5)

[0062] Although FIGS. 2A and 2B are described with respect to anoxygen-containing medium, other mediums containing other elementscapable of generating radical species in the presence of electron holepairs will be apparent to those of skill in the art. One such medium isa nitrogen-containing medium. Others include reagents that may reactacross an unsaturated bond via a Michael-type addition mechanism.

[0063] Referring now to FIG. 2C, photosensitizer Ph is excited fromground state P⁰ to excited singlet state ¹p* by energy quanta E₃.Photosensitizer Ph decays from singlet state ¹p* to intermediate excitedtriplet state ³p* While disposed in the triplet state, photosensitizerPh is able to transfer energy to another triplet state molecule. Somemolecules have a triplet ground state, for example, oxygen O₂, which isused in the exemplary embodiment of FIG. 2C.

[0064] As seen in FIG. 2C, energy is transferred from excited tripletstate photosensitizer ³p* Ph to triplet ground state oxygen molecule³O₂, thereby exciting the ³O₂ molecule to an excited singlet state ¹O₂.A radical-generating reaction may then be achieved with the excitedsinglet state molecule ¹O₂, for example, a reaction that generatesoxygen-containing radical species. Other molecules capable of formingradical species upon exposure to an excited photosensitizer will beapparent to those of skill in the art, for example, thiohydroxamicesters.

[0065] With reference to FIG. 3, oxidation of a surface coating in thepresence of radical species is described. It should also be noted thatoxidation may be possible with excited singlet or triplet statemolecules, in addition to radical species. In FIG. 3A, oxidizablesurface coating C, disposed on substrate Su, is contacted by radicalspecies R. Radical species R causes surface coating C to locally oxidizewhere the radical species contacts the surface coating at point P, asseen in FIG. 3B. The cross-section of point P may be on the order ofangstroms or smaller.

[0066] The chemistry of coating C may be chosen such that the reactivityof the coating may be altered at point P, and may either stabilize ordestabilize point P of coating C. For example, dependent on thechemistry of coating C and/or secondary processing techniques, point Pof coating C may be removed from coating C, as seen in FIG. 3C.Alternatively, coating C may be removed from substrate Su at allpositions except point P, as seen in FIG. 3D.

[0067] With reference now to FIG. 4, a first embodiment of apparatus inaccordance with the present invention is described. Apparatus 30comprises substrate 32 having surface 34 with oxidizable coating 36.Apparatus 30 further comprises mask 40 having mask section 42 andpattern section 44. Photocatalyst layer 46 is disposed beneath masksection 42 and pattern section 44. Apparatus 30 also comprises energysource 50. Apparatus 30 still further comprises medium M in whichoxidizable coating 36 and photocatalyst layer 46 are immersed. Mask 40is disposed between substrate 32 and energy source 50.

[0068] Mask section 42 of mask 40 preferably comprises a shieldingmaterial, for example, a UV or x-ray absorber or quencher, carbon, or ametal such as lead, or gold, which is capable of inhibiting transmissionof energy irradiated by energy source 50. Mask section 42 may alsocomprise a material capable of quenching radical species, such asselenium or zinc. Additional materials for mask section 42 will beapparent to those of skill in the art.

[0069] Pattern section 44 comprises the portion of mask 40 defining thepattern to be replicated on surface 34 of substrate 32. In FIG. 4A,pattern section 44 comprises either a material capable of transmittingenergy provided by energy source 50, or voids formed within mask section42, for example, drilled within mask section 42 to expose photocatalyticsemiconductor layer 46. Pattern section 44 further comprises theportions of layer 46 disposed beneath such voids or transmittingmaterial.

[0070] Photocatalyst layer 46 may comprise a photocatalyticsemiconductor layer, a photosensitizer layer, or a combination thereof.For the purposes of the present invention, a photocatalyst is defined asa material that is capable of producing a photochemical and/orphotophysical alteration in a system, without being consumed by thealteration. When the photocatalyst comprises a photocatalyticsemiconductor, TiO₂ is a preferred photocatalytic semiconductor, butothers, such as SnO₂, or an InTaO₄ compound doped with Ni, will beapparent to those of skill in the art and are included in the scope ofthe present invention. When the photocatalyst comprises aphotosensitizer or photosensitizing agent, preferred photosensitizersinclude photofrins, texaphyrins, metallotexaphyrins, porphyrins,hematoporphyrins, chlorins, bacteriochlorins, phthalocyanines andpurpurins. Additional photosensitizers will be apparent to those skilledin the art and are included in the present invention.

[0071] It is also contemplated that substrate 47 may be attached to mask40, as seen in FIG. 4B. Substrate 47 may be attached either to layer 46,as in FIG. 4B, or to the shielding material of mask section 42. Withsubstrate 47 attached to layer 46, mask 40 is preferably positioned suchthat mask section 42, as well as the transmitting portion of patternsection 44, is disposed closest to coating 36, while layer 46 isdisposed between the shielding layer and the substrate. A preferredsubstrate comprises fused silica or quartz, however other substrateswill be apparent.

[0072] A variety of materials and techniques may be used to form mask 40having mask section 42 and pattern section 44. In a first embodiment,mask 40 is formed as a bilayer material. The first layer comprises ashielding material, as described above with respect to mask section 42.The second layer comprises the photocatalyst layer 46, also describedpreviously. Optionally, substrate 47 may be included as a third layer. Aportion of the shielding layer is then selectively removed, for example,using e-beam or traditional machining techniques, to expose layer 46 andform pattern section 44, as well as mask section 42.

[0073] In a second embodiment, mask 40 is formed ofPoly(dimethylsiloxane) (“PDMS”). In this embodiment, PDMS mask 40 may bedipped in a solution of the photocatalyst just after curing.Alternatively, the photocatalyst may be painted, flame-coated, or vapordeposited on the surface. Portions exposed to the photocatalyst comprisepattern section 44, while other portions comprise mask section 42.

[0074] In a third embodiment, mask 40 comprises polymers, such asPolyvinyl chloride (“PVC”) or polyethylene terephthalate. As with PDMS,polymer masks 40 may be selectively dipped in a solution containing thephotocatalyst, or the photocatalyst may, for example, be painted,flame-coated or vapor deposited on the surface. For polymers that aregood transmitters, UV stabilizers may be incorporated in/on the mask atall points outside of pattern section 44, thereby forming mask section42.

[0075] In a fourth embodiment, mask 40 comprises a glass. A preferredtechnique for depositing photocatalyst layer 46 on the glass is throughchemical vapor deposition (CVD). As in FIG. 4B, an additional shieldingmaterial may also be deposited. Additional, alternative materials forforming mask 40, as well as additional deposition techniques for formingmask section 42 and pattern section 44, will be apparent to those ofskill in the art.

[0076] When using a photocatalytic semiconductor layer 46, energy source50 preferably comprises a UV or x-ray lamp or laser. Energy source 50generates energy quanta above the band gap of photocatalyticsemiconductor layer 46. When using a photosensitizer layer 46, energysource 50 preferably comprises a visible light source, such as a lightsource with a wavelength between about 550-850 nm, for example, avisible laser light source, such as a Helium Neon (“HeNe”) laser. Energysource 50 is capable of exciting photosensitizer layer 46. Other energysources will be apparent to those of skill in the art. Energy source 50may be pulsed in order to control an extent of radical generation anddiffusion.

[0077] Medium M preferably comprises a medium capable of generatingradical species in the presence of electron hole pairs or excitedmolecules, such as an oxygen- or nitrogen-containing medium. Medium Mmay be either organic or inorganic and is preferably fluidic, forexample, a gaseous medium, a liquid medium, an aqueous medium, a gel,water, or air. Furthermore, medium M preferably comprises an oxidant,such as oxygen, nitrogen, oxidizing ions, Redox species, Redoxmediators, or electron transfer agents. The medium may also oralternatively contain stabilizing agents, such as selenium, zinc, lipoicacid, methionine, cysteine, or N,N Dimethyl glycine. As yet anotheralternative, medium M may comprise more inert conditions, such as vacuumor argon gas, in which case elements capable of generating radicalspecies are attached to substrate 30 or mask 40. Other mediums will beapparent to those of skill in the art.

[0078] Referring to FIG. 5, in conjunction with FIGS. 2-4, a method forusing the apparatus of FIG. 4 is described. As seen in FIG. 5A, mask 40is brought into close proximity or contact with surface 34. Energysource 50 is activated and irradiates mask 40 with incident light 52.Mask section 42 of mask 40 inhibits incident light 52 from irradiatingsurface 34. However, where incident light 52 strikes pattern section 44of mask 40, it generates radical species. As discussed previously withrespect to FIGS. 2A and 2B, when photocatalyst layer 46 comprises aphotocatalytic semiconductor, electron hole pairs are generated withinthe photocatalytic semiconductor because incident light 52 excites layer46 with energy above the band gap of the semiconductor. As discussedpreviously with respect to FIG. 2C, when photocatalyst layer 46comprises a photosensitizer, incident light 52 excites thephotosensitizer in a manner capable of generating radical species uponcontact with appropriate molecules, for example, oxygen molecules orthiohydroxamic esters.

[0079] The electron hole pairs or excited molecules generate radicalspecies R at the interface of medium M and layer 46. Radical speciestypically are capable of traveling on the order of 100 nm. It isexpected that radical species R will be transferred from the interfaceof medium M and layer 46 to the interface of medium M and oxidizablecoating 36 of surface 34 along a substantially shortest distance path.As seen in FIG. 5B, and discussed previously with respect to FIG. 3, theradical species locally oxidize coating 36 to form pattern 44′ onsurface 34 of substrate 32. Pattern 44′ replicates the shape of patternsection 44 of mask 40 on surface 34.

[0080] Such local patterning through chemical modification of coating 36is expected to alter the reactivity of the coating, and may eitherstabilize or destabilize pattern 44′. Unaffected adsorbed materialoptionally may be used for a second chemical step, for example, a secondmasking step.

[0081] Coating 36 may, for example, be used in a manner similar to thepositive and negative resist coatings used in photolithography, asdiscussed hereinabove with respect to FIG. 1. Thus, coating 36 may beremoved at all points on surface 34 disposed within pattern 44′, forexample, via a secondary rinse. Alternatively, coating 36 may be removedat all points on surface 34 that are not disposed within pattern 44′.

[0082] A significant advantage of the present invention, as compared toprior art photolithography techniques, is that the portion of patternsection 44 of mask 40 comprising photocatalyst layer 46 is expected toenable patterning of features in coating 36 of surface 34 that aresignificantly smaller than the wavelength of light generated by energysource 50. When using a photocatalytic semiconductor, this is possiblebecause the radical species generated via photocatalytic semiconductorlayer 46 have a dimension on the order of sub-angstroms, as compared toincident light 52, which has a dimension on the order of nanometers.Likewise, when using photosensitizers, the radical species generatedwith photosensitizer layer 46 are expected to be significantly smallerthan the wavelength of incident light. Thus, pattern section 44 of mask40 is preferably capable of patterning surfaces with features havingresolutions less than about 100 nm, and even more preferably less thanabout 10 nm. Resolution of pattern 44′ may be controlled, for example,by controlling the size of features within pattern section 44, and/or bycontrolling the distance between mask 40 and surface 34.

[0083] Another significant advantage of the present invention is that itis expected that the methods and apparatus described herein may be usedin conjunction with a variety of oxidizable surface coatings 36. In afirst embodiment, the surface coatings comprise alkane thiols. Alkanethiols are described in greater detail in U.S. Pat. Nos. 4,690,715 toAllara et al., 5,512,131 to Kumar et al., 5,686,548 to Grainger et al.,6,020,047 to Everhart, 6,183,815 to Enick et al., and 6,048,623 toEverhart et al., all of which are incorporated herein by reference. In asecond embodiment, the coatings comprise thioethers. Thioethers,including their oxidation characteristics and their capabilities forselective modification, are described in greater detail in U.S. patentapplication Publication Ser. No. 2003/0,059,906 to Hubbell et al., aswell as pending U.S. patent application Ser. No. 10/246,362 to Hubbellet al. (corresponding to PCT publication WO 03/024897), filed Sep. 18,2002, and U.S. patent application Ser. No. 10/246,500 to Hubbell et al.(corresponding to PCT publication WO 03/024186), filed Sep. 18, 2002,all of which are incorporated herein by reference. In a thirdembodiment, the coatings comprise unsaturated materials, i.e. materialscomprising double or triple bonds. Coatings comprising reactivesaturated materials are also contemplated, for example, materialscomprising chlorine or bromine. In yet another embodiment, the surfacecoatings comprise metallic oxides, or bare metal substrates capable ofoxidizing. Other coatings will be apparent to those skilled in the art.

[0084] In an alternative embodiment of apparatus 30, mask section 42 ofmask 40 is removed. As seen in FIG. 4C, photocatalyst layer 46 isdeposited directly onto substrate 47 in a desired pattern, therebyforming pattern section 44. Removal of mask section 42 is significant inthat many oxidizable surface coatings 36 would spontaneously oxidize inthe presence of incident light 52 of adequate power. For this reason,mask section 42 provides shielding in the embodiments of FIGS. 4A and 4Bto ensure that energy of incident light 52 only reaches surface 34indirectly via radical species generated in pattern section 44.

[0085] In this alternative embodiment, the energy and power of incidentlight 52 generated by energy source 50 is specified such that, whenusing a photocatalytic semiconductor, the excitation energy delivered byincident light 52 is above the band gap of photocatalytic semiconductorlayer 46; alternatively, when using a photosensitizer, energy deliveredby incident light 52 is capable of exciting photosensitizer layer 46 toa singlet state. Furthermore, the excitation energy of incident light 52preferably is specified such that it is below the power typicallyrequired to cause spontaneous oxidation of oxidizable surface coating36. Thus, incident light 52 that passes through mask section 42 of mask40, without contacting photocatalyst layer 46, irradiates coating 36without causing oxidation. Oxidation still only occurs locally atlocations on surface 34 that are contacted by radical species generatedwithin pattern section 44, i.e. oxidation only occurs within pattern 44′of surface 34.

[0086] When using a photocatalytic semiconductor layer 46, the band gapenergy of the photocatalytic semiconductor is dictated by:

E=hv   (6)

[0087] where h is Plank's constant and equals 1.603×10⁻¹⁹, and E is theband gap energy of layer 46. Since v is the frequency of incident light52, and is related to the wavelength λ of the incident light by:

ν=C/λ  (7)

[0088] where C equals the speed of light, the excitation energy ofincident light 52 can be specified such that it is above the band gapenergy E of photocatalytic semiconductor layer 46 by choosing an energysource 50 capable of generating incident light 52 of appropriatewavelength. As an example, when layer 46 comprises TiO₂, the band gapenergy is 3.2 eV, which may be generated by the wavelength of lightproduced with either a UV or x-ray energy source 50.

[0089] Next, it is believed that the power required for spontaneousoxidation of coating 36 is dependent on Boltzmann's probabilisticequation, which follows an exponential decay law such that, for thepurposes of the present invention, a probability of oxidation isexpected to decrease with decreasing power. By maintaining a power levelhaving a low probability of spontaneously oxidizing the surface, it isexpected that selective patterning may be achieved with the alternativeembodiment of mask 40 described hereinabove. Reducing the amount of timewhich coating 36 is exposed to incident light 52 may also reduce aprobability of oxidation.

[0090] Although the equations above are believed to describe the bandgap energy of a photocatalytic semiconductor, and the probability of asurface coating oxidizing in appropriate media upon exposure to a givenpower level for a specified period of time, the present invention isprimarily concerned with the end result, i.e. patterning. Thus, theseequations are provided only for the benefit of the reader and should inno way be construed as limiting.

[0091] A significant advantage of the alternative embodiment of mask 40described with respect to FIG. 4C is that the criticality of excludingincident light 52 from surface 34 is reduced. Thus, increasedflexibility is obtained in designing mask 40. Furthermore, increasedflexibility is obtained in specifying the direction from which incidentlight 52 illuminates pattern section 44. This, in turn, increasesflexibility in the positioning of energy source 50. For example, in thisalternative embodiment, energy source 50 may illuminate pattern section44 from the side, from an angle, or from below mask 40, as compared tojust from above/through mask 40.

[0092] Referring now to FIG. 6, alternative embodiments of apparatus inaccordance with the present invention are described. In FIG. 6A, as withapparatus 30, apparatus 100 comprises substrate 32 having surface 34with oxidizable coating 36. Apparatus 100 also comprises energy source50 and medium M. Apparatus 100 still further comprises stamp 110 havingcontact section 112 and pattern section 114 with photocatalyst layer116. As with apparatus 30, when layer 116 comprises a photocatalyticsemiconductor, energy source 50 generates energy quanta above the bandgap of the photocatalytic semiconductor, and when layer 116 comprises aphotosensitizer, energy source 50 is capable of exciting thephotosensitizer. Oxidizable coating 36 and photocatalyst layer 116 areimmersed in medium M. Stamp 110 is disposed between substrate 32 andenergy source 50.

[0093] Contact section 112 is adapted to substantially contact coatedsurface 34 at all points along the interface of stamp 110 with surface34, except along pattern section 114. Contact section 112 preferablycomprises a shielding material and/or stabilizing or quenching agents onits underside at points that contact surface 34. However, contactsection 112 may alternatively comprise a material capable oftransmitting incident light 52 generated by energy source 50, or maycomprise a partially transmitting material.

[0094] When contact section 112 contacts coated surface 34, medium M ispreferably substantially excluded from the interface between the contactsection and the surface, thereby decreasing a likelihood of spontaneousoxidation of coating 36 due to irradiation with incident light 52.Pattern section 114 is preferably slightly recessed with respect tocontact section 112, such that medium M remains in the interface betweenpattern section 114 and oxidizable coating 36 of surface 34, whencontact section 112 contacts surface 34. The recession of patternsection 114 is preferably less than about 100 nm, which is on the orderof the distance that radical species are able to travel.

[0095]FIG. 6B provides an alternative embodiment of apparatus 100 inwhich contact section 112 of stamp 110 is replaced with transmissionsection 112′, which is recessed with respect to pattern section 114.Pattern section 114, meanwhile, substantially contacts surface 34. Inthis embodiment, medium M remains in the minute interface betweensurface 34 and pattern section 114, in order to facilitate radicalformation. It is expected that oxidation efficiency may increase as afunction of decreasing distance between photocatalyst layer 116 andoxidizable coating 36. Furthermore, if quenching species are disposed,for example, on the underside of masking section 112′, recession ofsection 112′ may decrease a likelihood of spontaneous oxidation ofcoating 36 via transmission of incident light 52 through masking section112′. Alternatively, when transmission section 112′ transmits incidentlight 52, the light may be tuned such that it excites photocatalystlayer 116, but does not induce spontaneous oxidation of coating 36 inthe presence of medium M, as described hereinabove with respect to FIG.4C.

[0096] With reference now to FIG. 7, a method of using the apparatus ofFIG. 6A to selectively pattern surface 34 is described. Although thismethod is described with respect to the apparatus of FIG. 6A, it shouldbe understood that a similar method may be used with the apparatus ofFIG. 6B, as will be apparent to those of skill in the art. As seen inFIG. 7A, stamp 110 is brought into contact with surface 34 such thatcontact section 112 of stamp 110 substantially excludes medium M fromthe interface between contact section 112 and surface 34. Medium Mremains in the interface between pattern section 114 and oxidizablecoating 36 of surface 34. Energy source 50 is then activated andgenerates incident light 52, which passes through stamp 110.

[0097] In pattern section 114, when photocatalyst layer 116 comprises aphotocatalytic semiconductor, incident light 52 generates electron holepairs within photocatalytic semiconductor layer 116. When photocatalystlayer 116 comprises a photosensitizer, incident light 52 excites thephotosensitizer. These electron hole pairs or excited photosensitizermolecules generate radical species in the presence of medium M that aretransmitted to surface 34 and locally oxidize coating 36 to form pattern114′ on surface 34. Pattern 114′ replicates the geometry of patternsection 114 of stamp 110 on surface 34, as seen in FIG. 7B.

[0098] In the preferred embodiment of contact section 112, the contactsection is shielded or quenched on its underside to prevent incidentlight 52 from irradiating coating 36 at points where contact section 112contacts the coating. In an alternative embodiment where contact section112 is not, or is only partly, shielded or quenched, incident light 52passes through contact section 112 and irradiates oxidizable coating 36of surface 34. Advantageously, even if the power of incident light 52 issufficient to spontaneously oxidize coating 36, since coating 36 issubstantially excluded from medium M at all locations along contactsection 112, the coating is unable to absorb the necessary moleculesrequired for oxidation, e.g. oxygen. Thus, coating 36 cannot oxidize atlocations in contact with contact section 112 that are excluded frommedium M, and it is expected that surface 34 may be selectivelypatterned regardless of whether contact section 112 transmits incidentlight 52.

[0099] As with apparatus 30, a significant advantage of apparatus 100and all embodiments of the present invention, as compared to prior artphotolithography techniques, is that it is expected that pattern 114′ onsurface 34 may contain features that are significantly smaller than thewavelength of light generated by energy source 50. This is possiblebecause the radical species generated via photocatalyst layer 46 have adimension on the order of sub-angstroms, as compared to incident light52, which has a dimension on the order of nanometers. Thus, patternsection 114 of stamp 110 is preferably capable of patterning surfaceswith features having resolutions less than about 100 nm, and even morepreferably less than about 10 nm. Resolution of pattern 114′ on surface34 may be controlled, for example, by controlling the size of featureswithin pattern section 114, and by controlling the distance that patternsection 114 is recessed with respect to contact section 112, therebyaltering dispersion of radical species.

[0100] Referring now to FIG. 8, yet another alternative embodiment ofapparatus in accordance with the present invention is described, whereinthe mask or stamp is replaced with a scanning probe. As with apparatus30 and 100, apparatus 150 comprises substrate 32 having surface 34 withoxidizable coating 36, as well as energy source 50 and medium M.Apparatus 150 further comprises scanning probe 160 having tip 162 withphotocatalyst layer 164. Scanning probe 160 is able to translate indirections 170, for example, the X-, Y-, and/or Z-directions.Alternatively, directions 170 may comprise the r-, θ-, and/orΦ-directions. Energy source 50 is coupled to tip 162 via coupling device166, which may comprise, for example, a fiber optic cable or anear-field optical microscopy aperture. As previously, energy source 50generates energy quanta capable of exciting photocatalyst layer 164 ofprobe 160, and oxidizable coating 36 and photocatalyst layer 164 areimmersed in medium M.

[0101] With reference to FIG. 9, a method of using the apparatus of FIG.8 to selectively pattern a surface is provided. Scanning probe 160 isbrought into close proximity or contact with surface 34, as seen in FIG.9A. Energy source 50 is activated, and incident light 52 travels throughcoupling device 166 to tip 162 of probe 160. Incident light 52 excitesphotocatalyst 164 thereby forming radical species in the presence ofmedium M, which are transmitted to oxidizable coating 36 along asubstantially shortest distance path. Oxidizable coating 36 oxidizeslocally at the point where these radical species contact surface 34,i.e. at a point substantially directly below tip 162 of probe 160,thereby forming selective pattern 162′ on surface 34, as seen in FIG.9B. As discussed previously, it is expected that the dimension ofpattern 162′ advantageously may be significantly smaller than thewavelength of incident light 52. Probe 160 may then be scanned ortranslated in directions 170 while energy source 50 is activated toprovide a dynamic pattern 162′, which may be specified by an operator inreal time, as seen in FIG. 9C.

[0102] The use of scanning probe 160 may be advantageous in someapplications because it provides highly localized oxidation of surface34. Additionally, the distance between probe tip 162 and surface 34 maybe finely adjusted to alter the resolution of pattern 162′, for example,by modulating dispersion of radical species between tip 162 and surface34. Furthermore, the resolution of pattern 162′ may be modulated byaltering the cross-section of layer 164 disposed on tip 162. Furtherstill, by translating scanning probe 160 in any plane, a vast variety ofselective patterns 162′ may be provided on surface 34, i.e. a variety ofpatterns may be oxidatively ‘carved’ or ‘painted’ into the surface. Anexemplary pattern 162′ formed by translating scanning probe 160, isprovided in FIG. 9C. Probe 160 may be translated at any desired rate,and/or with any desired power/energy parameters provided by source 50.Additionally, energy source 50 may be intermittently turned on and off,or pulsed, during translation of probe 160, thereby providing aselective pattern 162′ that is discontinuous (see FIG. 10D). Moreover,an array of scanning probes may be utilized, as is known in thelithographic arts.

[0103] Referring now to FIG. 10, a variety of exemplary selectivelypatterned surfaces are provided. It is expected that these patterns willbe achievable using any or all of apparatus 30, 100, or 150 describedpreviously, or with additional embodiments of the present inventionconstructed in accordance with the present invention.

[0104] As discussed previously, local patterning of surface 34 ofsubstrate 32 via chemical modification of coating 36 is expected toalter the reactivity of the coating, and may either stabilize ordestabilize the local pattern. Unaffected adsorbed material optionallymay be used for a second chemical step, for example, a second maskingstep.

[0105] Furthermore, coating 36 may, for example, be used in a mannersimilar to the positive and negative resist coatings used inphotolithography, as discussed hereinabove with respect to FIG. 1. Thus,coating 36 may be removed at all points on surface 34 disposed withinthe local pattern, for example, via a secondary wash, rinse, or etch.Alternatively, coating 36 may be removed at all points on surface 34that are not disposed within the local pattern.

[0106] For the purposes of FIG. 10, patterns refer to portions ofcoating 36 that have been removed from surface 34. In FIG. 10A, surface34 comprises local pattern 200 that was formed by a process similar to apositive resist. In FIG. 10B, surface 34 comprises a local pattern 202that was formed by a process similar to a negative resist. In FIG. 10C,which is shown in side-view, surface 34 comprises three-dimensionallocal pattern 204. Pattern 204 may be formed, for example, bycontrolling an extent of oxidation of coating 36 or by shaping surface34 prior to patterning. In FIG. 10D, surface 34 comprises discontinuouslocal pattern 206. In FIG. 10E, surface 34 comprises two-step localpattern 208 having first pattern 209 and second pattern 210. First andsecond patterns 209 and 210 may be formed, for example, with twoseparate masks or stamps.

[0107] While preferred illustrative embodiments of the invention aredescribed hereinabove, it will be apparent to one skilled in the artthat various changes and modifications may be made therein withoutdeparting from the invention. For example, the substrate or surface onwhich the oxidizable coating is disposed may be provided with a voltagebias, for example, an anodic bias, to facilitate selective patterning ofthe surface. As another example, a mask or stamp may be provided withtwo or more different photocatalyst layers. When providing multiplephotocatalytic semiconductor layers, each may comprise a different bandgap potential. When providing multiple photosensitizer layers, each maycomprise a different excitation energy. A mixture of photocatalytic andphotosensitizer layers may also be provided. In such embodiments,multiple energy sources may be provided, each capable of generatingenergy at a different excitation level. Alternatively, a tune-ableenergy source may be provided.

[0108] The mask or stamp may then be irradiated with incident light ofan energy capable of exciting the first photocatalyst layer, but not thesecond, different layer. This creates a first pattern on a targetsurface. A second pattern may then be provided by increasing theexcitation energy of the incident light generated by the energy sourceto a level above the excitation energy of the second photocatalystlayer, thereby creating a second pattern on the target surface. Anynumber of patterns may be provided with this technique using a singlestamp or mask. Alternatively, multiple masks or stamps may be used togenerate multiple surface patterns on a target surface. Further still,incident light may be exposed to a photocatalyst layer in successiveportions, thereby providing multiple surface patterns from a singlestamp or mask.

[0109] The appended claims are intended to cover all such changes andmodifications that fall within the true spirit and scope of theinvention. Additionally, it should be understood that, in order toemphasize important aspects of the present invention, the FIGS. areschematic and have not been drawn to scale.

What is claimed is:
 1. Apparatus for selectively patterning anoxidizable surface, the apparatus comprising: a photocatalyst; a mediumin communication with the photocatalyst and the oxidizable surface; andan energy source adapted to excite the photocatalyst, wherein thephotocatalyst generates radical species in the medium upon excitation bythe energy source.
 2. The apparatus of claim 1, wherein the oxidizablesurface comprises an oxidizable coating disposed on the surface.
 3. Theapparatus of claim 1, wherein the photocatalyst comprises aphotocatalytic semiconductor adapted to generate electron hole pairsupon excitation by the energy source, and wherein the electron holepairs generate the radical species in the medium.
 4. The apparatus ofclaim 1, wherein the medium is adapted to transport the radical speciesfrom the photocatalyst to the oxidizable surface.
 5. The apparatus ofclaim 1, wherein the radical species are adapted to locally oxidize thethe oxidizable surface at points where the radical species contact thesurface.
 6. The apparatus of claim 5, wherein locally oxidizing theoxidizable surface comprises locally pattering the surface.
 7. Theapparatus of claim 3, wherein excitation of the photocatalyticsemiconductor by the energy source comprises excitation above a band gapof the photocatalytic semiconductor.
 8. The apparatus of claim 1,wherein the photocatalyst is chosen from the group consisting ofphotocatalytic semiconductors, TiO₂, SnO₂, compounds of InTaO₄ dopedwith Ni, photosensitizers, photofrins, texaphyrins, metallotexaphyrins,porphyrins, hematoporphyrins, chlorins, bacteriochlorins,phthalocyanines, purpurins, and combinations thereof.
 9. The apparatusof claim 1 further comprising a delivery device on which thephotocatalyst is disposed.
 10. The apparatus of claim 9, wherein thedelivery device is chosen from the group consisting of stamps, masks,probes, scanning probes, and combinations thereof.
 11. The apparatus ofclaim 9, wherein the photocatalyst is disposed on the delivery device ina specified pattern.
 12. The apparatus of claim 11, wherein thespecified pattern comprises a pattern chosen from the group consistingof an entirety of the delivery device, a 2-dimensionally patternedsection of the delivery device, a 3-dimensionally patterned section ofthe delivery device, a tip of a scanning probe, a localized region ofthe delivery device, and combinations thereof.
 13. The apparatus ofclaim 11, wherein the specified pattern is fabricated using e-beamlithography.
 14. The apparatus of claim 1, wherein the energy source ischosen from the group consisting of visible light sources, UV sources,x-ray sources, visible light lamps, UV lamps, x-ray lamps, mercurylamps, visible light lasers, HeNe lasers, UV lasers, x-ray lasers,pulsed lamps, pulsed lasers, and combinations thereof.
 15. The apparatusof claim 1, wherein the oxidizable surface comprises a surface chosenfrom the group consisting of alkane thiols, thioethers, unsaturatedmaterials, saturated materials, bare metal surfaces, metal oxides, andcombinations thereof.
 16. The apparatus of claim 9 further comprising asecond photocatalyst disposed on the delivery device.
 17. The apparatusof claim 11, wherein the delivery device inhibits transmission ofexcitation energy provided by the energy source outside of the specifiedpattern.
 18. The apparatus of claim 1, wherein the medium comprises afluid medium.
 19. The apparatus of claim 1, wherein the medium comprisesan oxidant chosen from the group consisting of oxygen, nitrogen,oxidizing ions, Redox species, Redox mediators, electron transferagents, and combinations thereof.
 20. The apparatus of claim 1, whereinthe medium comprises a medium chosen from the group consisting ofgaseous mediums, liquid mediums, aqueous mediums, organic mediums,inorganic mediums, water, gels, air, oxygen-containing mediums,nitrogen-containing mediums, thiohexamic ester-containing mediums, Argongas, vacuum, and combinations thereof.
 21. The apparatus of claim 1further comprising a stabilizing agent.
 22. The apparatus of claim 21,wherein the stabilizing agent is chosen from the group consisting ofselenium, zinc, lipoic acid, methionine, cysteine, N,N Dimethyl glycine,and combinations thereof.
 23. A method for selectively patterning anoxidizable surface, the method comprising: providing a photocatalyst inclose proximity or contact to the surface; exciting the photocatalyst;generating radical species with the excited photocatalyst; transferringthe radical species to the surface; and locally oxidizing the surface atpoints where the radical species contact the surface, therebyselectively patterning the surface.
 24. The method of claim 23, whereinthe photocatalyst comprises a photocatalytic semiconductor, and whereinexciting the photocatalyst comprises forming electron hole pairs in oron the photocatalytic semiconductor.
 25. The method of claim 24, whereinforming electron hole pairs in or on the photocatalytic semiconductorcomprises exciting the photocatalytic semiconductor above its band gap.26. The method of claim 24, wherein generating radical species with theexcited photocatalyst comprises generating radical species with theelectron hole pairs.
 27. The method of claim 26, wherein generatingradical species with the electron hole pairs comprises generatingspecies by contacting the electron hole pairs with a medium incommunication with the photocatalytic semiconductor.
 28. The method ofclaim 23, wherein the photocatalyst comprises a photosensitizer.
 29. Themethod of claim 23, wherein transferring the radical species to thesurface comprises transferring the radical species to the surfacethrough a medium.
 30. The method of claim 23, wherein the mediumcomprises a fluid having an oxidant.
 31. The method of claim 23, whereinproviding a photocatalyst comprises providing a photocatalyst chosenfrom the group consisting of photocatalytic semiconductors, TiO₂, SnO₂,compounds of InTaO₄ doped with Ni, photosensitizers, photofrins,texaphyrins, metallotexaphyrins, porphyrins, hematoporphyrins, chlorins,bacteriochlorins, phthalocyanines, purpurins, and combinations thereof.32. The method of claim 23, wherein providing a photocatalyst comprisesproviding a photocatalyst disposed on a delivery device.
 33. The methodof claim 32, wherein providing a photocatalyst disposed on a deliverydevice comprises providing a photocatalyst disposed on a delivery devicechosen from the group consisting of stamps, masks, probes, scanningprobes, and combinations thereof.
 34. The method of claim 23, whereinlocally oxidizing the surface comprises locally oxidizing a surfacechosen from the group consisting of alkane thiols, thioethers,unsaturated materials, saturated materials, bare metal surfaces, metaloxides, and combinations thereof.
 35. The method of claim 23 furthercomprising: providing a second photocatalyst in close proximity orcontact to the surface; exciting the second photocatalyst; generating asecond set of radical species with the second excited photocatalyst;transferring the second set of radical species to the surface; andlocally oxidizing the surface at points where the second set of radicalspecies contact the surface, thereby selectively patterning the surfacewith a second pattern.
 36. The method of claim 35, wherein thephotocatalyst and the second photocatalyst comprise differentphotocatalysts.
 37. The method of claim 23, wherein selectivelypatterning the surface comprises selectively patterning the surface witha pattern chosen from the group consisting of positive patterns,negative patterns, continuous patterns, discontinuous patterns,multi-step patterns, one-dimensional patterns, two-dimensional patterns,three-dimensional patterns, and combinations thereof.
 38. The apparatusof claim 1, wherein a bias voltage is applied to the oxidizable surface.39. A patterned surface made by a process comprising: generating radicalspecies with a photocatalyst; and locally oxidizing the surface with theradical species to pattern the surface.
 40. The patterned surface madeby the process of claim 39, wherein generating radical species with thephotocatalyst further comprises generating radical species with aphotocatalytic semiconductor.
 41. The patterned surface made by theprocess of claim 40, wherein generating radical species with thephotocatalytic semiconductor further comprises forming electron holepairs in the photocatalytic semiconductor that form radical species uponexposure to appropriate media.
 42. The patterned surface made by theprocess of claim 39, wherein generating radical species with thephotocatalyst further comprises generating radical species with aphotosensitizer.
 43. The patterned surface made by the process of claim39, wherein generating radical species with the photocatalyst furthercomprises exciting the photocatalyst with an energy source.
 44. Thepatterned surface made by the process of claim 39, wherein locallyoxidizing the surface with the radical species to pattern the surfacecomprises patterning the surface with features having a size smallerthan about 100 nm.
 45. The patterned surface made by the process ofclaim 39, wherein locally oxidizing the surface with the radical speciesto pattern the surface comprises patterning the surface with aresolution finer than about 100 nm.
 46. The patterned surface made bythe process of claim 39, wherein generating radical species with thephotocatalyst further comprises generating radical species with aphotocatalyst disposed on a delivery device.
 47. The patterned surfacemade by the process of claim 46, wherein generating radical species witha photocatalyst disposed on a delivery device further comprisesgenerating radical species with a photocatalyst disposed on a deliverydevice chosen from the group consisting of stamps, masks, probes,scanning probes, and combinations thereof.
 48. The patterned surfacemade by the process of claim 46, wherein generating radical species witha photocatalyst disposed on a delivery device further comprisesgenerating radical species with a photocatalyst disposed on a deliverydevice in a specified pattern.
 49. The patterned surface made by theprocess of claim 48, wherein generating radical species with aphotocatalyst disposed on a delivery device in a specified patternfurther comprises generating radical species with a photocatalystdisposed on a delivery device in a specified pattern that has featureswith a size smaller than 100 nm.
 50. The patterned surface made by theprocess of claim 48, wherein locally oxidizing the surface with theradical species to pattern the surface comprises transferring theradical species from the specified pattern on the delivery device to thesurface along a substantially shortest distance path.
 51. The patternedsurface made by the process of claim 39, wherein generating radicalspecies with a photocatalyst further comprises generating radicalspecies with a photocatalyst chosen from the group consisting ofphotocatalytic semiconductors, TiO₂, SnO₂, compounds of InTaO₄ dopedwith Ni, photosensitizers, photofrins, texaphyrins, metallotexaphyrins,porphyrins, hematoporphyrins, chlorins, bacteriochlorins,phthalocyanines, purpurins, and combinations thereof.